As improvement of automation technologies, the industry began to manufacture and assemble products by using the intelligent automation based on robot systems to improve the yield and the product quality. For example, the robot arms are introduced to applications of welding, cutting, dispensing and assembly. It is essential to maintain reliability of production, high repetition, and absolute accuracy in a long-term process in order to meet the requirements of the product quality. However, any errors that occur in the robot systems or the peripheral equipment thereof lead to shut down the production line. Great amount of time and money will be wasted. Therefore, errors and mechanical deviation caused by a long-term operation or repair shall be eliminated by the accuracy calibration. In addition to off-line calibration, users may directly calibrate robot arms in the production line (in-line) to save time and labors of dismantle, transport, and assembly. In general, most of the robot manufacturers do not provide services of calibration at a customer's factory or an on-site service. The users have to dismantle and transport the robot systems back to the original equipment manufacturers by ocean shipping or air transportation, which is time consuming and costly. Currently, only a few companies provide simple on-site calibration. Most of the robot systems still have to be disassembled and then sent back to the original equipment manufacturers in local or airlifted to the foreign equipment manufacturers. The service of high accuracy calibration or on-site calibration is difficult to widespread since one of the reasons is the expensive and huge factors of the calibration equipment. In the industry chain, lacking of absolute accuracy calibration becomes a restriction to develop a production line with a high precision.
In general, before shipment, robot arms will be calibrated and tuned repeatedly to meet an absolute precision. The robot arms will work at the absolute precision at the beginning. But after a prolonged use, the precision of the robot arms is hard to maintain because of mechanical deviation. The mechanical deviation may be caused by metal fatigue or repair such as replacement of motors or gears. Absolute accuracy calibration may solve these problems to ensure the precision ranges in a reasonable interval and improve the reliability in production lines.